Thermal overload relay



Sept. 10, 1940. L, P|ERE 2,214,626

THERMAL OVERLOAD RELAY Filed June 16, 1938 WITNESSES:v INVENTOR 507 MW L arr/@2768 P/brca 1 fin Ma 264 ATTORNEY Patented Sept. 10, 1940 THERMAL OVERLOAD RELAY Lawrence Pierce, Edgewood, rs, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa, a corporation oi Pennsylvania Application June 16, 1938, SerialNo, 214,037 1 Claims., 101100-122) ,of small current carrying capacity such as aregenerallyused in connection with thermal overload relays of the bimetallic disc type. In the operation of thermal overload relays of the type that utilize an electrically heated bimetallic disc to open a pair of contacts in a coil circuit for the disconnection of power upon the occurrence of an overload in electric motors, and

in numerous other applications, such as in providing group fusing for a number oi motors, the electric heaters used may be permitted to burn out but when such burn-out" occurs, no damage must be done to other elements of the relay or adjacent relays. In accordance with best practice, the relay should be protected against shortcircuits by fuses rated at no more than four times the rated motor current by a properly set time limit circuit-breaker. Heaters available in present day constructions are of two varieties; namely, of the open type and the closed type. Heaters of theopen type are a source of frequent trouble, for when the heaters burn out due to short-circuit or abnormal overloads, ionized gas circulates around the working parts. When using the totally enclosed type, the explosive force, or pressure, resulting from the heater burning out, has little chance of being released and in consequence considerable physical damage results.

According to my invention, I eliminate the defects in prior art heater constructions by providing a construction which permits the explosive gases to escape readily and to prevent the spewing of the hot metal in the region of the thermo-static member or disc which may clog up as a result. Briefly, I provide a ioraminous enclosure for the heater by placing a gauze-like 40 element over a cup recess which contains the heater member and hold it in place by some well known manner, for example, by the use of a shield which may be securely fastened to the relay casing. By such construction, the screen or gauze-like element sets up a cooling or deionizing action in the region of the heater so that the explosive gases become harmless in escaping through the gauze.

It is therefore an object of my invention to provide a novel heater assembly for a thermal of a foraminous enclosure for an electric heater of a thermal relay.

Other objects and advantages of my invention will become more apparent from a study of the following detailed description taken in conjunction with the accompanying drawing in which:

Figure 1 illustrates a vertical sectional view of a. thermal overload relayshowing the heater element, screen, and a shield in place according to my invention;

Fig. 2 illustrates, according to my invention, a side view of the removable heater, shield, supporting member, and the metal screen mounted on the supporting member;

Fig. 3 shows a side view of the metal screen only; and

Fig. 4 shows a plan view of the shield which is fastened over the screen to the supporting member.

' Referring more particularly to Fig. 1 of my invention, I show a thermal overload relay 3, with which my invention may be practiced. The relay members, which include a. thermostatic element, or disc 5, a heater assembly I, and separating contacts 9, are directly or indirectly secured to .a casing H of some suitable insulating material. The heater assembly I which is easily removable, includes a loop-shaped resistor l3 and a supporting member IS. The loopshaped resistor l3 of the heater assembly 1 is mountable in a cylindrical cup recess ll formed in the casing II and is held in spaced relation to the bimetallic disc 5, which is secured in place in the bottom of the cup recess ll, The resistor l3 itself is fastened to the casing l l by means of a set of screws or binding posts IS. The wiring circuit for the heater is not illustrated as it is immaterial to the present invention. Nevertheless, the heating resistor I3 is connected directly in the circuit of the device that is to be protected and the amount of heat generated by the resistor i3 is a function of the amount of current flowing.

The thermostatic member 5 is essentially a convex bimetallic disc which quickly reverses its convexity when heated to a predetermined temperature. In changing its position, the disc 5 causes the opening of a pair of contacts 9 where-' by power is disconnected from the device that is to be protected. With the heater assembly 1, properly mounted in place, a metal screen 2|, shown in full view in Fig. 3, of gauze-like fineness and having an opening 23 in its central portion, is disposed, as shown, with reference to the cup recess l1 and is preferably held in place by placing a plate-like shield 25 over the heater assembly I. This shield has a plurality of vent openings 21 and a central opening-29. A rivet or small bolt and nut 3| secures the shield 25 of the right-hand end of member I3.

and the screen or foraminous disc 2| to the support IS.

The screen 2| used in the practice of my invention may be preferably eight one-thousandths of an inch thick, though the stated dimensional characteristics are not absolutely essential.

One of the essential features of my invention is that when the heating resistor ll burns out upon the occurrence of a short-circuit, the gauzelike element or foraminous disc 2| produces a cooling and a deionizing effect, so that the explosive gases do not affect any of the other relay members, nor cause short-circuits. In reducing the pressure, the molten metal is kept from being thrown behind the working parts of the relay 3, particularly the bimetallic disc 5 which may be easily clogged.

How my supporting structure, or member, I5 and the foraminous covering, or screen, 2| accomplish the novel results may probably be readily apparent from an inspection of Fig. 1. However, for added clarity of the disclosure the following is submitted:

In the event of an excessive overload or shortcircuit, the heater disintegrates. Since the disintegration begins at the least ventilated portion, it will begin to disintegrate first at the arcuate surface of the member Hi. The products of disintegration, gases and molten particles, from the nature of the arcuate surface alone, will be thrown into the region to the left of the righthand end of member l3 and not toward the right Further, since the thermostatic element 5 completely closes the right-hand end of the cylindrical cupshaped portion supporting the spider at the left of the element 5, and the element 5, the structure is generally that of a shell for a gun. When heater l3 explodes, the pressure almost instantaneously builds up at the right of heater l3 and since there is substantially no obstruction to fluid flow toward the left, the gases and molten particles are thrown toward the left and thus do not injure any of the working parts of the relay.

In the normal operation of the heating resistor I3, the metal screen 2| prevents dirt from entering the cup recess l1 and contacting the hot resistor |3 thus reducing the fire hazards."

My invention is, of course, not to be limited to the particular shape and design of the perforated member 2| as other forms and designs would equally serve the purposes of my invention.

Although I have shown and described certain specific embodiments of my invention, it will be apparent that changes and modifications may be made therein without departing from the true spirit and scope of my invention. I desire, therefore, that only such limitations be imposed as are embodied in the accompanying claims or as may be necessitated by the prior art.

I claim as my invention:

1. In a removable electric heater assembly for a thermal device, the combination of, a loop shaped resistor constituting a heater, a supporting structure therefor, said thermal device having a cup recess providing space for mounting said resistor, a gauze-like member covering the opening of said cup recess, and means for securing said gauze-like member in place, said supporting structure engaging the inner and bottom portion of the heater so that in the event the heater dislntegrates because of an excessive overload, the explosive gases, or volatile matter, are directed away from the thermal device and directed toward said gauze-like member to facilitate in the cooling of the gases.

2. In combination, a thermo-electric responsive device having a cup recess, a bimetallic disc disposed in the base of said cup recess and relay means actuated by said disc, a removable electric heater assembly comprising a loop-shaped resistor constituting a heater, a supporting structure therefor, said loop-shaped resistor being mountable in said cup recess so as to be in spaced relation with reference to said disc, a gauze-like element covering the mouth of said cup recess, an opening in the central portion of said gauze and means extending through said opening for also securing said gauze-like element to said supporting structure, said supporting structure engaging the inner and bottom portion of the heater so that in the event the heater disintegrates because of an excessive overload, the explosive gases, or volatile matter, are directed away from the thermal device and directed .toward said gauze-like member to facilitate in the cooling of the gases.

3. A removable electric heater for a thermal responsive device, the combination of a loopshaped resistor constituting a heater, a supporting structure therefor, said device having a cup recess providing space to mount said resistor, a gauze-like member covering the mouth of said cup portion and a plate shield forsupporting said gauze-like member in place, said shield having a plurality of openings, said supporting structure engaging the inner and bottom portion of the heater so that in the event the heater disintegrates because of an excessive overload, the explosive gases, or volatile matter, are directed away from the thermal device and directed toward said gauze-like member to facilitate in the cooling of the gases.

4. In a thermally operated relay, in combination, a temperature responsive element for operating the relay, an electric heater for the temperature responsive element, a shell-like structure open at one end housing the heater and a foraminous cover for said open end of the shelllike structure.

5. In a thermally operated relay, in combination, thermo-electric means adapted to operate said relay, a shell-like housing, open at one end, for said means, and a foraminous cover for the open end of the shell-like structure associated with said thermo-electric means.

6. A removable electric heater for a thermal responsive device, the combination of a resistor constituting a heater, a cup-shaped supporting structure for the heater, said device having a foramlnous cover for the structure for providing space to enclose said heater.

7. A thermo-electric responsive device comprising, in combination, a supporting structure of insulating material, a temperature responsive element secured to said structure, a heater element mountable to be in proximity to said temperature responsive element, said heater enclosed in a casing of which a lesser portion of the wall of said casing is composed of a foraminous material.

LAWRENCE PIERCE. 

